This invention broadly concerns the detection and semi-quantitative measurement of the flow of solids. More particularly, it concerns the flow of divided solids in small diameter tubes at high pressures. In one aspect of the utility of this invention, it can be used to measure a low rate of flow of crushed coal in a small diameter tube at a high pressure.
One prior art method of measuring a flow of solids concerns a pressure drop measurement, such as in a coal transport line. Broadly, this concerns the measurement of the change in pressure (.DELTA.P) at separated points along the tube. Experience shows that this method is not reliable because the high pressure (.DELTA.P) transmitters capable of withstanding wide pressure fluctuations are not sensitive enough to measure the pressure. And this method is not applicable to a low flow rate of solids in small diameter lines or tubes.
Another prior art method concerns the measurement of the enthalpy balance/temperature. This involves, for example, heating a transport gas stream to about 200.degree. F. upstream of where the gas is mixed with the coal, which is at ambient temperature. Then, when the coal flow starts, the temperature of the mixture downstream of the mixing point decreases. The upstream and downstream temperatures are then compared by thermocouples, referenced to each other, with the temperature difference being displayed on a recorder. This method has been found somewhat unreliable due to drift, caused by small ambient and process variations affecting the temperature readings. Also, at low flows of transport gas and coal, the signal-to-noise ratio gives unreliable readings, because the low flow of coal does not carry enough heat to give an appreciable temperature differential (.DELTA.T) over the ambient readings.
I have found that my invention overcomes or avoids these disadvantages and that low flow rates of solids in a small diameter tube, at high pressures and high temperatures, can be detected and semi-quantitatively measured.